Field of the Invention
Preferred embodiments relate to the art of a control system for hybrid vehicles in which a motor is used not only to control an engine speed but also to generate a drive force for propelling the vehicle.
Discussion of the Related Art
U.S. Pat. No. 5,788,006 to Yamaguchi describes a so-called “dual motor type” hybrid vehicle provided with a planetary gear unit functioning as a differential gear system. In the planetary gear unit, a carrier is connected to the engine, a sun gear is connected to a first generator/motor, and a ring gear is connected to a differential unit through a counter gear unit. The counter gear unit is also connected to a second motor so that the second motor is allowed to be activated by an electric power supplied from the first generator/motor. The differential gear system is allowed to serve as a speed reducing device by stopping a rotation of an input shaft connected to the carrier by a brake so that torque of the first generator/motor applied to the ring gear can be multiplied.
US2011/0230292 A1 also describes a vehicle drive apparatus similar to the hybrid vehicle taught by U.S. Pat. No. 5,788,006. In the drive apparatus of this kind, the carrier is halted when the vehicle is towed while stopping the engine, and hence pinion gears and pinion pins may not be lubricated sufficiently. In order to avoid such a disadvantage, according to the teachings of US2011/0230292 A1, the drive apparatus is provided with a lubricant receiver having a lubricating passage connecting a fluid retainer situated above a planetary gear unit with the pinion gears.
As described, in the hybrid vehicle taught by U.S. Pat. No. 5,788,006, the differential gear system is allowed to serve as the speed reducing device by stopping a rotation of the carrier by the brake while stopping the engine. Consequently, the multiplied torque of the first generator/motor can be transmitted to wheels through the ring gear to propel the vehicle. In this situation, however, lubricant would not be lifted by the carrier, and hence the pinion gears and the pinion pins may not be lubricated sufficiently.
As also described, the vehicle drive apparatus taught by US2011/0230292 A1 is provided with the lubricant receiver having the lubricating passage connecting the fluid retainer with the pinion gears. In the drive apparatus taught by US2011/0230292 A1, therefore, the pinion gears etc. may be lubricated sufficiently if sufficient amount of the lubricant is retained in the retainer. However, if the remaining lubricant in the retainer is nearly exhausted or if viscosity of the lubricant is high, the pinion gears etc. may not be lubricated sufficiently. In addition, significant modification is required to install such additional lubricant receiver in the drive apparatus, and consequently, the vehicle drive unit would be enlarged.
Aspects of preferred embodiments have been conceived noting the foregoing technical problems, and it is therefore an object of various preferred embodiments to provide a drive control system for hybrid vehicles, which limits damage to a planetary gear unit to extend duration of an electric propulsion mode in which the vehicle is powered by a motor connected to a power distribution device.